Field of the Invention
The present invention relates to the art of a vibration damper for suppressing torque pulses (i.e., vibrations) by an inertial torque.
Discussion of the Related Art
U.S. Pat. No. 5,863,274 describes a torsional vibration damping apparatus comprising a planetary transmission in which a sun gear serves as an input element, and a carrier or a ring gear serves as an output element. In the planetary transmission, the sun gear is connected to a first mass, and the carrier or the ring gear is connected to a second mass. According to the teachings of U.S. Pat. No. 5,863,274, coil springs are interposed between any of two rotary elements of the planetary transmission in such a manner as to permit an angular displacement therebetween to an extent which depends upon the extent of deformation of the coil springs.
The planetary gear unit used in a vibration damper is also described e.g., in JP-A-2009-14022 and JP-A-2010-1905. In the inertia device taught by JP-A-2009-14022, the planetary gear unit is used to obtain a large inertia force by increasing rotational speed of an inertia ring to be higher than an input speed. In turn, in the rotation fluctuation reduction device taught by JP-A-2010-1905, one of rotary elements of the planetary gear unit is connected to an output shaft of an engine to serve as an input element, other rotary element is attached to an inertial mass, and still another rotary element is selectively halted by a brake. According to the teachings of JP-A-2010-1905, an inertia torque counteracting torsional vibrations of the output shaft can be changed by halting a rotation of predetermined rotary element by the brake.
In the above-explained prior art documents, an inertial force counteracting vibrations is established by an inertial mass connected to any of the rotary elements of the planetary gear unit, and such inertial force can be increased by enlarging the inertial mass. According to the teachings of the above-explained prior art documents, however, the inertial masses are arranged in an axial direction of the planetary gear unit, and hence an axial length of the planetary gear unit may be elongated if the inertial masses are enlarged. Consequently, the vibration damping device may not be fitted into a powertrain easily.